1. Field
This disclosure is concerned generally with the binding of biologically active compounds to the surfaces of cells and specifically with a method of using cell receptors for the Fc domains of antibodies to control such binding.
2. Prior Art
Information about the binding of biologically active substances at the surfaces of cells has been increasing at a rapid rate, especially as new techniques for isolating and studying cell surface receptors sites have become available. While there is still much to be learned, it is now well known that many biological substances work or activate the generation of other substances by binding at so-called receptor sites at the surfaces of certain cells. More information on such cell receptor sites can be found, for example, in Alberts et al Molecular Biology of the Cell, 2nd ed, Garland Publishing, Inc. New York, 1989, pp 693-726.
In some cases, very small amounts of a biologically active substance can have a significant biological effect and very few cell surface receptors are needed. For example, in the case of the cytokine known as tumor necrosis factor (TNF), a very potent inflammatory mediator, it is known that the cells that respond to TNF have relatively few TNF receptor sites. See, for example, Beutler and Cerami, Ann. Rev. Immunol. 7:625-55, 1989. See also, U.S. Pat. No. 4,603,106 to Cerami et al, describing the isolation of a mediator referred to as cachetin and now known as TNF.
Among the other biologically active substances that have a relatively potent effect relative to their respective amounts are the various cytokines (e.g., IL1, IL2, and IL6), hormones (e.g., insulin, somatotropin, and adrenocorticotropic hormone, also known as ACTH) and growth factors (e.g., nerve growth factor, epidermal growth factor and fibroblast growth factor.) It should be understood that the above list of representative species is illustrative and by no means intended to be complete.
The function of all cells is governed by receptor interactions with these and other biologically active substances. These substances may act at a site distant from their site of origin (e.g., insulin made in the pancreas effects carbohydrate metabolism in the liver), or these substances may act locally, sometimes effecting the same cell which produces them (e.g., T cells both produce and respond to IL2) (See, for example, Alberts et al, pp 682-694, 1046-1047). Clearly, in the micro-environment of the cell surface, fluctuations in the amount of biologically active substances regulate cell function. In the case of potent cytokines and inflammatory mediators, high levels of these substances may have disastrous consequences; e.g., septic shock (Beutler and Cerami, Ann. Rev. Immunol. 7:625-55, 1989). In these cases it would be highly desirable to control the level of these substances in the micro-environment of the cell surface.
In cells where there are relatively few surface receptors for a given substance, the options available for influencing the amount of substance in the micro-environment of the cell surface are somewhat limited. However, it is known that many cells that have a limited number of specific receptors also have available receptors for the Fc domain of antibodies (See, for example, Mellman et al, J. Cell. Sci. Suppl. 9:45-65, 1988). In many cases, the number of these Fc domain receptors is many-fold greater than the limited number of substance receptors.
Taking into consideration the fact that some cells have receptor sites for both a given substance and the Fc domain of antibodies, we have now found methods for influencing the amount of substance in the micro-environment of such cells. This is done by exploiting the Fc receptors by using antibodies specific to the substance, or conjugated antibodies that include at least some antibodies specific to the substance. Details of our methods and examples using such antibodies are described below.